The present invention relates to a crankshaft milling machine having at least one milling unit which is controllable in its feed advance by a copying mechanism operating in synchronism with the rotation of the work piece.
Prior art crankshaft milling machines of this type have a guide for the milling unit and the guide defines a plane located below the work piece and substantially horizontally. Further, the milling unit is arranged on a second guide also extending horizontally and perpendicularly to the longitudinal axis of the work piece. The milling unit is controlled in its feed advance by a so-called copying mechanism. Reference is made in this connection to a publication entitled "Werkstatt und Betrieb" Volume 110, H.3, 1977, pages 137 to 145.
The disadvantages of horizontally extending guides in crankshaft milling machines are well known. A guide in this position primarily hinders the removal flow of milled-off chips. Additionally, the horizontal guide makes the access to the machine difficult for exchanging the work piece as well as the milling tool.
Thus, it is known to use guides in turning lathes which define a plane extending on one side of the work piece and in parallel to the work piece axis as well as substantially in a vertical plane so that the chips milled-off during the operation may bypass the guide to fall downwardly. Additionally, the space between the work piece clamping chuck or vise is freely accessible from one side in the sense that the operator may enter into the space between the work piece clamping means without even having the possibility of stepping onto components of the machine tool.
However, in connection with crankshaft milling machines, such machines which may be referred to as vertical bed machines have not yet been considered. The milling units of crankshaft milling machines have a substantial weight. Thus, the feed advance drive would have to either be capable to move the substantial weight of the milling unit up and down or a respective weight balancing would have to be provided. Such weight balancing would relieve the feed advance drive of the weight of the milling unit. However, such weight balancing means would entail a substantial additional expense.
German Utility Model No. 7,106,698 describes a different type of crankshaft milling machine in which the milling unit is tiltable about a swivel axis extending in parallel to the axis of the work piece and located below the work piece axis. Additionally in this prior art milling machine the feed advance drive is also located below the swivel axis so that the entire machine has an unnecessary structural height. Additionally, the feed advance drive hindered the chip removal flow as well as the accessibility of the inside of the machine to an extent more than is the case in the known horizontal bed milling machine. Thus, the structure disclosed in German Utility Model No. 7,106,698 has not found any acceptance in practice.
German Pat. No. 957,711 describes a copying milling machine for turbine blades or vanes in which the milling unit is tiltable about a swivel axis extending in parallel to the work piece axis. Additionally, the feed advance drive for the milling unit is arranged on the side of the work piece facing away from the swivel axis. In this type of milling machine the swivel axis was substantially located in the same horizontal plane as the work piece axis so that the feed advance drive was required to balance the weight of the milling unit as described above. Such an arrangement is possibly acceptable in connecting with copying milling machines for turbine blades because the milling units in such machines have a relatively small weight, without inviting problems. However, in connection with crankshaft milling machines this type of structure is not acceptable because the milling units in crankshaft milling machines have a substantial weight relative to the weight of the entire machine structure.
In prior art machines it was not possible to achieve a closed force flow around the work piece so that the milling forces had to be taken up or conducted through the machine bed or frame. Thus, the use of these measures in connection with milling machines having a guide bed extending about vertically is not possible without difficulties. Such difficulties are seen in that the vertical bed would have to be of a correspondingly solid construction. Such solid construction would even further increase in three directions the good sound damping characteristics of these machines. However, such improvement would require an additional expense which could not be justified from an economical point of view.